REG 316*4 1MRB520049-Uen / Rev. F ABB Switzerland Ltd
3-25
3.5. Protection functions
3.5.1. Transformer differential protection function (Diff-Transf)
A. Application
Differential protection of two and three-winding power trans-
formers generator/transformer units.
B. Features
· Non-linear, current-dependent operating characteristic
(see Fig. 3.5.1.1)
· High stability during through-faults and in the presence of c.t.
saturation
· Short tripping times
· Three-phase measurement
· Inrush current restraint
· using the second harmonic
· detection of the highest phase current
· detection of the load current to determine whether the
transformer is energised or not
· Compensation of phase group
· Compensation of c.t. ratio
· Scheme for three-winding transformers
· phase-by-phase comparison of the highest winding cur-
rent with the sum of the currents of the other two windings
· d.c. current component filter
· harmonic filter.
C. Inputs and outputs
I. C.t./v.t. inputs:
· Current (2 or 3 sets of 3 inputs)
II. Binary inputs:
· Blocking
III. Binary outputs:
· tripping
· R phase trip
· S phase trip
· T phase trip
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